Rheology control agents (RCAs) and their uses are known in the art. RCAs are incorporated into coating compositions primarily to improve resistance to sag, i.e., rheology control. RCAs present in the prior art include bis urea crystals, which are the reaction product of a diisocyanate and an amine, and fumed silica.
These conventional RCAs, and other RCAs, have proven to be inadequate for incorporation into coating compositions for a variety of reasons. For instance, fumed silica RCAs are inert relative to the cross-linking agent of the coating composition. That is, these conventional RCAs do not react with the cross-linking agent. As a result, these conventional RCAs do not participate in the cross-linking reaction to further enhance the integrity of the film produce upon application and cure of the coating composition. Furthermore, primarily because there is no chemical reaction, i.e., cross-linking, between the conventional RCAs and either the resin or the cross-linking agent, these conventional RCAs are frequently detrimental to other properties of the film including, but not limited to, adhesion, re-coat adhesion, and appearance.
Although other conventional RCAs, such as bis urea crystal RCAs, are reactive with the cross-linking agent, these conventional RCAs are inadequate because they require highly stringent manufacturing and processing specifications to achieve optimum rheology control in the coating composition. For instance, bis urea crystal RCAs must have a certain particle size and also must be finely dispersed into a resin to achieve optimum rheology control. Bis urea crystal RCAs are also highly sensitive to polar solvents and, as a result, lose most of their rheology control in the presence of alcohols which are commonly incorporated into coating compositions.
Finally, the levels at which the RCAs of the prior art are incorporated into coating compositions to be effective in resisting sag are frequently so high that the VOC content of the coating composition is impractical for application in industry.
In sum, the RCAs of the prior art, including those described above, are characterized by one or more inadequacy. Due to the inadequacies identified in the prior art, it is desirable to provide a novel rheology control agent that is reactive with a cross-linking agent in a coating composition and that resists sag while maintaining other properties of the coating composition and of a film of the coating composition.